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mutable objects as default arguments

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rasbt 2014-04-15 17:10:19 -04:00
parent e361912537
commit 38092ac583
2 changed files with 146 additions and 4 deletions
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75
.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
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@ -1,7 +1,7 @@
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@ -45,7 +45,8 @@
"- [Picking True values from and and or expressions](#false_true_expressions)\n", "- [Picking True values from and and or expressions](#false_true_expressions)\n",
"- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n", "- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n",
"- [Be aware of the consuming generator](#consuming_generator)\n", "- [Be aware of the consuming generator](#consuming_generator)\n",
"- [`bool` is a subclass of `int`](#bool_int)" "- [`bool` is a subclass of `int`](#bool_int)\n",
"- [About lambda and closures-in-a-loop pitfall](#lambda_closure)"
] ]
}, },
{ {
@ -583,6 +584,76 @@
], ],
"prompt_number": 16 "prompt_number": 16
}, },
{
"cell_type": "markdown",
"metadata": {},
"source": [
"<br>\n",
"<br>\n",
"<a name='lambda_closure'></a>\n",
"\n",
"## About lambda and closures-in-a-loop pitfall\n",
"\n",
"The following example illustrates how the (last) `lambda` is being reused:"
]
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"my_list = [lambda: i for i in range(5)]\n",
"for l in my_list:\n",
" print(l())"
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{
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"source": [
"**Here, a generator can save you some pain:**"
]
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"my_gen = (lambda: n for n in range(5))\n",
"for l in my_gen:\n",
" print(l())"
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75
not_so_obvious_python_stuff.ipynb
View File

@ -1,7 +1,7 @@
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@ -45,7 +45,8 @@
"- [Picking True values from and and or expressions](#false_true_expressions)\n", "- [Picking True values from and and or expressions](#false_true_expressions)\n",
"- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n", "- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n",
"- [Be aware of the consuming generator](#consuming_generator)\n", "- [Be aware of the consuming generator](#consuming_generator)\n",
"- [`bool` is a subclass of `int`](#bool_int)" "- [`bool` is a subclass of `int`](#bool_int)\n",
"- [About lambda and closures-in-a-loop pitfall](#lambda_closure)"
] ]
}, },
{ {
@ -583,6 +584,76 @@
], ],
"prompt_number": 16 "prompt_number": 16
}, },
{
"cell_type": "markdown",
"metadata": {},
"source": [
"<br>\n",
"<br>\n",
"<a name='lambda_closure'></a>\n",
"\n",
"## About lambda and closures-in-a-loop pitfall\n",
"\n",
"The following example illustrates how the (last) `lambda` is being reused:"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"my_list = [lambda: i for i in range(5)]\n",
"for l in my_list:\n",
" print(l())"
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{
"output_type": "stream",
"stream": "stdout",
"text": [
"4\n",
"4\n",
"4\n",
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"4\n"
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},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Here, a generator can save you some pain:**"
]
},
{
"cell_type": "code",
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"input": [
"my_gen = (lambda: n for n in range(5))\n",
"for l in my_gen:\n",
" print(l())"
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